The present invention generally relates to superconducting devices, and more specifically relates to reducing the number of input lines to superconducting quantum processors installed inside dilution refrigerators using frequency-division-multiplexing components.
The phrase “superconducting quantum computing” refers to the use of a quantum computer in superconducting electronic circuits. Quantum computation studies the application of quantum phenomena for information processing and communication. Various models of quantum computation exist, and the most popular models incorporate the concepts of qubits and quantum gates. A qubit can be thought of as a generalization of a bit that has two possible states but can be in a quantum superposition of both states. A quantum gate can be thought of as a generalization of a logic gate in that the quantum gate describes the transformation from their original state that one or more qubits will experience after the gate is applied on them. The physical implementation of qubits and gates can be difficult to implement, for the same reasons that quantum phenomena are hard to observe in everyday life. One approach is to implement the quantum computers in superconductors where the quantum effects become macroscopic, though at a price of extremely low operation temperatures.
Superconducting quantum computer are typically designed to work in the microwave frequency range, cooled down in dilution refrigerators below 100 milliKelvin (mK), and communicated with (e.g., addressed with) using conventional electronic instruments. Typical dimensions of qubits are on the scale of micrometers, with sub-micrometer resolution, and allow a convenient design of a quantum Hamiltonian (which is an operator corresponding to the total energy of the system) with the well-established integrated circuit technology. An example of a dilution refrigerator that can be used in the above-described cooling process is a 3He/4He dilution refrigerator, which is a cryogenic device that provides continuous cooling to temperatures as low as 2 mK, with no moving parts in the low-temperature region. The cooling power is provided by the heat of mixing the Helium-3 and Helium-4 isotopes. It could be considered the only continuous refrigeration method for reaching temperatures below 0.3 K. Modern dilution refrigerators can precool the 3He with a cryocooler in place of liquid nitrogen, liquid helium, and a 1 K bath. No external supply of cryogenic liquids is needed in these “dry cryostats” and operation can be highly automated. Dry dilution refrigerators generally follow one of two designs. One design incorporates an inner vacuum can, which is used to initially precool the machine from room temperature down to the base temperature of the pulse tube cooler (using heat-exchange gas). However, every time the refrigerator is cooled down, a vacuum seal that holds at cryogenic temperatures needs to be made, and a low temperature vacuum feed-through must be used for the experimental wiring. The other design is more demanding to realize because it requires heat switches for precooling. However, the other design does not require an inner vacuum can, which greatly reduces the complexity of the experimental wiring.